1. Field of the Invention
The present invention relates to two-component, polyurethane compositions containing hydroxyl-functional polydimethylsiloxanes and to their use for preparing coatings, adhesives or sealants.
2. Description of Related Art
2K (two-component) PU (polyurethane) paints and coatings combine high mechanical strength with effective resistance to solvents and chemicals. On the basis of their outstanding technological properties, 2K PU paints and coatings are employed for a multiplicity of applications from a very wide variety of fields, such as large-vehicle finishing, automotive refinish, coil coating, corrosion control, floor coating, and adhesives.
The modification of 2K PU paint systems with polydimethylsiloxanes (PDMS) is known. The high surface tension of PDMS produces specific properties, such as good surface wetting, slip resistance and an easy-to-clean surface (Reusmann in Farbe und Lack, 105, volume 8/99, pages 40-47; Adams in Paintindia, October 1996, pages 31-37).
In order to ensure effective incorporation of PDMS and to substantially prevent migration of the PDMS, organofunctional PDMS types, such as alkyleneamine- or alkylenehydroxyl-functional PDMS derivatives, are often used. Paint systems of this kind are described for example in WO91/18954, EP-A 0 329 260 or U.S. Pat. No. 4,774,278.
The amine-functional PDMS types, however, have the disadvantage that the pot life of polyurethane systems based on them is extremely abbreviated, due to the high propensity to form ureas.
Although the known hydroxyl-functional PDMS types give improved pot lives, they generally exhibit incompatibilities with the polyisocyanate component, meaning that homogeneous films cannot be produced and that crosslinking is incomplete. As a result there is free, unbound PDMS in the paint, which migrates over time from the coating and leads to a deterioration in the coating's properties.
U.S. Pat. No. 6,475,568 describes the use of copolyols obtained by reaction of epoxy- functional PDMS oligomers and primary or secondary amines as an additive for cosmetics products or fabric softeners. The use of these compounds for preparing 2K PU binders for paints and coatings is not described.
WO 2004/022619 describes the use of chain extenders for polyurea systems which are obtained by reacting epoxy-functional PDMS with amines. The reaction of epoxy-functional PDMS with hydroxylamines to form the corresponding OH-functional compounds is not described.